Papers by Keyword: Melt Infiltration

Abstract: Over the last years, new alloys were developed to create metallic glasses showing high crystallization temperatures. Such metallic glasses generally can be embedded into other materials when processing temperatures are lower than crystallization temperatures. As recent studies show, feasible crystallization temperatures may exceed the melting point of common metals and fabrication of metallic glass particle reinforced MMCs is now not only possible by powder metallurgical methods but also by processes using melt infiltration. Hence, these metallic glasses offer a high potential for use as reinforcements in a lightweight metal matrix such as aluminum: By incorporation of metallic glass structures into a ductile matrix, it is possible to utilize its outstanding advantages like high strength and elastic strain limit while circumventing its negative properties like brittleness.The particle reinforced composites in this contribution were produced by gas pressure infiltration. This process includes melt infiltration of a particle filled mold using pressurized gas. To keep a sufficient separation between processing temperature and crystallization temperature, the metallic glass Ni₆₀Nb₂₀Ta₂₀ (T_x = 721 °C) and the eutectic aluminum alloy AlSi12 with a low melting point (T_m = 580 °C) as matrix metal were selected for process. After infiltration, the fabricated MMCs were investigated by micro computed tomography (µCT) to analyze the particle distribution within the composite. Furthermore, mechanical tests and elastic analysis using ultrasound spectroscopy were performed to classify its properties.

Abstract: Porous TiC-Ni3Al performs were fabricated by using Ni, Al, Ti and graphite powder with self-propagating high-temperature combustion synthesis (SHS) method. Then, the porous perform were infiltrated with melt Ni3Al via the conventional pressureless infiltration process to prepare TiC/Ni3Al composites. Effects of the infiltration temperature and time on the microstructure, hardness and wear resistance of the composites were studied. XRD, SEM and EDS were used to analyze the phase identification and the solubility of Ni3Al and TiC in each other. The results show that pressureless melt infiltration is an effective method to fabricate dense TiC/Ni3Al composites. The infiltration time can greatly decrease when the infiltration temperature suitably increases. No obvious effect of the infiltration temperature and time on the hardness and the wear resistance of the composites were found. Ni3Al and TiC were well bonded, and they are the only two phases in the composites after infiltration. The wear resistance of TiC/Ni3Al composites including 70% and 80% TiC were promoted 3.25 and 4.33 times compared with pure Ni3Al, respectively.

Abstract: Copper and 2024 aluminum alloy were melt-infiltrated into porous β-SiC to form SiC/Cu and SiC/Al composites. The porous β-SiC was prepared using Moso bamboo as the bio-template and had structural characteristics of bamboo. The Cu infiltration occurred as low as 1100°C and became significant at 1200°C. After infiltration at 1300°C for 4 h, there was still ~5 % of residual porosity. For the composites with low degree of metal infiltration, the samples fractured like the bamboo-structured porous SiC. For the composites with high degree of infiltration, the sample behaved like monolithic copper. In the infiltration of Al alloy, infiltration occurred at 900°C. Higher Infiltration temperatures would result in significant formation of Al4C3, which gradually decomposed in air.

Abstract: A novel process, of melt infiltration combined with diffusion annealing technique, was developed to prepare Ti-Al intermetallics at temperature lower than ingot melting point. In this process, a porous Ti preform was firstly fabricated and the Al melt was reheated to temperature slightly higher than Al melting point to infiltrate the porous Ti preform by capillary force spontaneously. After long-time high-temperature diffusion annealing, Ti-Al intermetallic compound can be finally synthesized from the bulk Tip+melt Al via diffusion. As example, Ti-46Al intermetallics has been fabricated, and the microstructures and the phases of the as-synthesized intermetallics were characterized by XRD and SEM. The compressive behavior of the as-synthesized Ti-Al at elevated temperatures has been studied and the reaction mechanism involved in the process finally analyzed.

Abstract: Two different types of carbon fibre bundles were used for filament winding to obtain C/C preforms. C/C-SiC composites were produced from the C/C preforms by a silicon melt infiltration technique. The effect of the type of carbon fibre bundle on the mechanical and thermal properties of the resultant C/C-SiC composites was compared. The spun fiber preform yields C/C-SiC composites of better mechanical properties than the unidirectional continuous fiber preform. The strength of the composites from the SFP was 1.8 times higher than that from the CFP. The flexural strength and the O-ring strength of the composites from the SFP with a density of 2.35 g/cm3 were about 160 MPa and 170 MPa, respectively.

Abstract: Alumina/glass composites were successfully fabricated by melt-infiltration of glass into porous alumina pellets. Alumina powder was first pressed uniaxially at 100MPa to form disc-shaped pellets, then, heated up to 1200°C for 2 h to form porous pellets with moderate strength for subsequent infiltration. A mixture of calcium aluminosilicate and magnesium borosilicate glass powders were melt-infiltrated into porous alumina at 1200°C ~1250°C by capillary pressure to form composites. The infiltration depths varied with the square root of infiltration time. And the activation energy of the infiltration process was estimated to be 621 KJ/mole. After complete infiltration, the composite had bulk density approaching 3.3 g/cm3 (~ 96% of theoretical density) and open porosity reaching zero, with slight expansion of 0.5% in diameter. Its flexural strength was 150MPa and its Vickers microhardness was about 1000 Kg/mm2.